Roller seems to have done a pretty good job of suppressing comment spammers. The math question seems to trip up automated scripts and I only get about 1 or 2 spam comments per month. At least, I only see 1 or 2 per month - many get marked as spam and just sit in the database - never to be displayed. However, recently I've started to notice a lot of Trackback spam.
I dive into my "comment" table a few times a week to format comments so they look like their author intended them to look (I never alter wording). In the past couple of weeks, I've noticed a buttload of spam trackbacks (up to 10-20 per day). Here is an example. How do we go about stopping trackback spam? I'm guessing the easiest way is to disable trackbacks.